For a long time, microorganisms such as bacteria, yeasts or fungi were considered non-complex organisms that could easily be eradicated with antimicrobials. However, today we are confronted with an alarming growth of disease-causing microbes that can no longer efficiently be controlled by available antibiotics or antifungals. This phenomenon is generally referred to as “antimicrobial resistance” or AMR. Clinicians in many different disciplines are experiencing difficulties to treat patients due to ineffective antimicrobials.
The impact of AMR is also evidenced by the problem of infections acquired during a stay at a healthcare related institution (hospitals, elderly care) also known as “nosocomial infections”. To combat the spread of AMR, there is an increasing pressure towards a more rational use of antibiotics. As a result, almost every Western country has launched campaigns to make people aware that misuse of antimicrobials makes them ineffective. In fact, the problem of AMR has grown to such a dramatic level that the World Health Organization moved it to the top-3 of global health risks.
Hence, there is a continuous need for new antimicrobial compositions, or agents that increase sensitivity of micro-organisms towards existing antimicrobials in order to combat the spread of AMR. A particular way of sensitizing microorganisms for certain antimicrobials is by interfering with their quorum sensing system.
Microorganisms such as bacteria use quorum sensing to coordinate certain behaviors such as biofilm formation, virulence, and antibiotic resistance, based on the local density of the bacterial population. Quorum sensing (QS) can occur within a single bacterial species as well as between diverse species, and can regulate different processes, in essence, serving as a simple indicator of population density or the diffusion rate of the cell's immediate environment. Several non-peptide small molecules, peptides and proteins have been shown to affect quorum sensing in bacteria and are suitable in the prevention and/or treatment of bacterial infections. For example hamamelitannin (HAM) or 2′,5-di-O-galloyl-D-hamamelose, a natural compound found in the bark and leaves of Hamamelis virginana (witch hazel), was found to act as a quorum sensing inhibitor (QSI) (WO2007147098). HAM interferes with a quorum sensing system in bacteria. It was found that when combining HAM with an antibiotic, a potentiating or synergistic effect is observed, in particular HAM increases the susceptibility of bacterial biofilms to antibiotics in vitro as well as in vivo (Brackman et al., 2011).
It is important to emphasize that HAM may not be considered as a classical antibiotic drug, since it does not exert bactericidal nor bacteriostatic effects. HAM probably interferes with mechanisms that are responsible for the exceptional resistance in biofilms and thus can cause a potentiating or synergistic effect in combination with antibiotics.
The natural HAM product is metabolically unstable and only moderately active, and therefore less preferable in the treatment of microbial infections. Nevertheless, interesting results obtained with this molecule provide a conspicuous lead for further optimization, and present an opportunity for the development of a novel class of pharmaceutical compounds, capable of combating microbial infections. It was therefore an object of the present invention to provide novel non-carbohydrate, drug-like HAM analogues with an improved metabolic and chemical stability and increased activity. Furthermore, we have developed an efficient synthetic route to produce these novel compounds from easily available starting materials.